The invention pertains to a method for spinning and washing aramid fiber and for recovering sulfuric acid, using a spinning unit and a sulfuric acid recovery unit.
Aramid fiber is normally produced by dissolving PPTA (para-phenylene terephthal-amide) polymer in 100% sulfuric acid after which the resulting spin dope is expelled through a spinneret. Sulfuric acid is then removed from the fibers in a washing step using water, resulting in a diluted solution of approximately 10-15% H2SO4.
The diluted sulfuric acid solution can be neutralized and disregarded, resulting in a considerable emission of sulfates and the use of considerable amounts of sulfuric acid and water from an external source. Therefore, it is more convenient to recycle it. For instance, it can be concentrated to 96% H2SO4 in a series of different distillation processes. Such process, however, is energy consuming and may cause a considerable stream of effluents. Water is evaporated from the sulfuric acid solution in the process, requiring considerable amounts of energy. Moreover, the distilled water contains trace amounts of sulfuric acid making it unsuitable for use as common water. It is therefore an objective to device a method for recovery and recycling sulfuric acid obtained during the spin process of aramid that uses low amounts of energy and can be performed in a closed system.